


The Devil You Know

by LadyKalan



Category: Fire Emblem Series, Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: AU kinda not really, Alternate Universe of sorts, Attraction, Canon Compliant, Character Study, Gen, Golden Deer Path, Relationship Study, Spoilers, Spoilers for Golden Deer Path, Supposed one-sided attraction, graphic depiction of confusion, headcanons but they're really minor, his flabber is completely gasted right now, someone tell our boy what's going on
Language: English
Status: Completed
Published: 2019-08-18
Updated: 2019-08-18
Packaged: 2020-08-10 13:07:42
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,444
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20135944
Author URL: https://archiveofourown.org/users/LadyKalan/pseuds/LadyKalan
Summary: Moderate Spoilers for the Golden Deer Path. Information is referenced up to the timeskip.Claude couldn't look away. Wearing black head to toe, with pink details, and a longcoat/cap with slit sleeves; they in no way looked like the simple mercenary they were supposed to be. But even their unique appearance wasn't what grabbed the noble's attention. It was their eyes.





	The Devil You Know

**Author's Note:**

> Inspired by Hanneman's C Support, Jeralt's diary, and Claude's curiosity. This is my take on one way to make Byleth just a bit more interesting.

The moment they met... Claude didn't actually pay any attention to them.

Despite their unusual hair and intricate outfit, they somehow blended perfectly into the background, completely unnoticed. From the moment Jeralt_ addressed_ them, however, Claude couldn't look away. Wearing black head to toe, with pink details, and a longcoat/cap with slit sleeves; they in no way looked like the simple mercenary they were supposed to be. But even their unique appearance wasn't what grabbed the noble's attention. It was their eyes.

Claude knew all about eyes. _He had to._ If he didn't learn to read a person's intentions through their eyes; he would have been killed from one of _numerous_ assassination plots _years_ ago. He used to focus on body language, but so did everyone else. And once everyone else learned to fake that, the emotions in their eyes were the only thing the teen could rely on. Yes, eyes were Claude's speciality. Which was why looking into this stranger's, and seeing_ nothing,_ set off every alarm bell he had.

It wasn't that the mercenary was hiding their thoughts, or that they were indifferent to the situation, he would still see_ something_ if that were the case. No, there was simply nothing there. Their gaze was empty. The kind of empty Claude had only ever seen in a _dead man's_ eyes.

The noble's first reaction was: **get away from this person as fast as possible. Danger! Stay away!** But, after he fought down that instinctual fear, it was his curiosity that threatened to drown him. He _had_ to know more about this enigma. _Every_ secret needed to be uncovered. He'd never be able to rest otherwise.

Thankfully, the gods of fortune truly were smiling down on him, as they were talked into coming to the Monastery with their father. Their father** Jeralt the Blade Breaker** of all people! Claude's search for the Hero Relics could wait a while longer. Learning _everything_ about this, mystery merc, was quickly taking priority.  
. . .  
The first important thing Claude learned about the new Professor, was that asking them about their past was meaningless.

They somehow knew _nothing_ about themself. Not that their father was a knight (the most famous knight in recent history how did they not know that?!), nothing about their mother, no prominent childhood memories, not even how old they were. It was incredibly frustrating, and also somehow, really _sad._

Claude didn't get the impression that Byleth didn't know these things, because they were purposely withheld from them. But rather that they simply never _cared_ enough about such things, to ever think to ask. It was absolutely baffling.

The teen had met some apathetic loners in his life. It took him a while, but he eventually learned the appeal of that lifestyle. If you don't care, you feel no pressure to do or act a certain way. It's freeing, to rid yourself of potential burdens and responsibilities. The Professor, however, was beyond apathy.

_Nothing_ seemed to get a reaction out of them. _No one_ mattered enough to make them want to emote. Not even their own _father._ It was one thing to not care, it was another thing entirely to lack the _ability_ to care, to lack emotions all together. Sometimes, watching the teacher made Claude feel like he was watching a walking corpse. And the more the golden boy was able to compare Byleth to a _dead body,_ the more unsettled he became.

His danger radar blared nonstop around the Professor. Yet, he couldn't bring himself to stay away. The more unknowable the former mercenary became, the more Claude _needed_ to know everything. Something _had_ to have happened in Byleth's past, to make them like that. Because the way they were was not normal, not _natural._ It wasn't... _**human.**_  
. . .  
The next thing Claude learned, was that Byleth, was a model teacher. No, they were a model _human being._

They held one on one tutoring sessions with every student, every week, without fail. They shared meals with students and staff alike, and it was always somehow one of both of their favorites. They helped to cook those very meals with the Head Chef's guidance. They offered moral support at each tournament, for both sides that were fighting. Sang with the choir in the chapel, _specifically_ so Marianne wouldn't be too uncomfortable to go. They helped in the greenhouse with Bernadetta. The _ultimate recluse_ Bernadetta. Found and returned lost items to everyone; sometimes before the person even _knew_ it was missing. And they knew what belonged to whom, with just a glance, every single time. They ran errands for anyone who asked (and _a lot_ of people asked). Answered all the questions in the advice box; and gave decent, _helpful_ answers at that. Made friends with the merchants to secure discounts for everyone else, but never for themself. They even stood with the Gatekeeper, whenever he got lonely. Byleth was** goodwill incarnate**, and Claude was _terribly confused._

How could someone with a dead gaze, someone so lifeless, so seemingly emotionless; be such a kind, generous, helpful individual? They wouldn't be, they _couldn't_ be. Such behavior forced the noble to reevaluate _everything_ he thought he learned about his Professor. <strike>But, only _after_ he spent an entire day berating himself, for judging a person by their appearance, instead of their actions; like he'd been fighting _against_ his whole life, real smooth Claude, real smooth</strike>.

No truly apathetic person would willingly do so much for so many people, especially not so consistently. Obviously Byleth did care, _deeply,_ about everything and everyone around them. Which made their empty expression all the more out of place. And made Claude even more curious.  
. . .  
So curious, in fact, that less than a month into school, he swallowed his apprehension, and went to the one person who could possibly have answers for him.

The teen still couldn't figure out what was in his eyes, as he entered the room. But whatever it was, it enough for Jeralt to take one look at him, sigh, and put down his paperwork. "So you're first, huh? I'm surprised a lot more people haven't come to me yet. Close the door, and I'll answer what I can."

Claude expected many things when he approached the most famous knight in recent history: defensive deflection, outright refusal to answer, complete dismissal of his presence, maybe even death glares and weighted silence. What he did not expect, was for that man to be _waiting_ for his questions.

Something about how,_ open,_ such an important person was to his probing, made the noble drop every facade he usually had set up. The teen allowed his smile to fall, he let himself fidget as he sat down, and it took him a few minutes into the conversation, to be able to actually look at the former captain in front of him.

"So, where should I start?"

"Um, well... I guess their eyes are what I'm most curious about."

"The lack of expressions, right? I'm afraid there's nothing terribly interesting to say about that. They've been that way since they were born, and even the doctors couldn't explain it."

"Oh..."

"But, don't let Byleth's blank face fool you. Expressionless doesn't mean emotionless. They have just as many feelings as the rest of us."

Claude already figured that out, but having it confirmed eased his nerves somewhat. "Really?"

"Uh-huh. It took me a couple years to be able to tell their feelings apart. The key wasn't in their face, or even their voice. It was their posture, their stances, that gave them away. They're very slight differences, and I had to squint for them at first, but once I could read those, everything else fell into place."

"That's... Thank you, I'll definitely remember that."

"Sure, sure... Anything else?"

"Oh, uh, why does no one know how old-"

"21"

"-they... I'm sorry?"

"They're 21, as of 5 months ago."

"You... But, if you know, then...?"

"Why don't they? I know it's not much of a reason, but they never asked. Well alright, they did once, when they turned 9, but after that... Clearly through the years they forgot, or stopped counting, and then they never asked again. I understand why it's such a weird concept to everyone else, but since the kid themself didn't care, I saw no reason to keep telling them."

"I figured it was something like that... You're right it is very weird."

Before the teen could say anymore, the church bell echoed through the room, signalling the end of the day. "There's, _a lot_ more that I want to ask. But, I think I have enough to think on for now." The former captain nodded once, and went back to his paperwork. "If you have any other questions, you know where to find me."

"Thank you." Although Jeralt wouldn't see it, Claude still followed his urge to bow, before he left the room. To do any less felt ungrateful.

As the young noble strode back to his room, he thought back to all the little movements he'd notice his teacher do. A shuffle of feet, a raised or lowered shoulder, a tilt or turn of the head. Little fidgets he'd noted, and never thought on again. He, of course, knew all about body language, and the information one can learn from it. But, body language was the first thing the people around him learned to fake.

Practicing and overriding movements was easy enough. Masking the feelings behind your eyes, however, proved to be far more difficult. It's why Claude studied eyes so intently, and why he learned to ignore body language so completely. To the point that he didn't even consider looking at it, when evaluating his teacher. He forgot that it was a viable option.

"What a cynical, one track mind I've developed. How foolish of me."  
. . .  
The next important thing Claude discovered, was how _terrifying_ his "Teach" could be.

Their first mission was to dispose of some bandits, which left a very bad taste in the teen's mouth. The first thing a _church_ is asking of it's _students,_ is to go _kill_ some people. There was a reason he wasn't too fond of big religions like these. Regardless, they had a mission to do, and they were all determined to do it.

It was still, difficult, to say the least, to watch his classmates' reactions, to what was clearly their first kill. Ignatz' shaky apology, Marianne praying so she didn't burst into tears, Lysithea rationalizing the act to herself, Hilda hiding her remorse behind her genuine surprise at her own strength. Leonie, Lorenz, and Raphael truly seemed happy to reach such a milestone. But even they couldn't hide how their hands shook.

But, all of the feelings Claude held about his classmates, meant nothing compared to his reaction to the teacher themself.

He didn't expect anything to be different than when they first met. And for the most part, it wasn't. Teach would draw the bandits' attention, and a small group would surround them while they're preoccupied with fighting. Once everyone understood the strategy, two groups were made, and sent in each direction. Byleth went ahead of both parties, to scout the area and look for traps. At least, that's what they _said_ they were doing.

For the first time since they'd met, Claude could feel that his Professor was lying, or at least giving a half truth. There had been, _something,_ different about them since they entered the Red Canyon. A feeling radiating off of them, almost tangible. Though _what_ that feeling was, the noble couldn't identify. Against his better judgement, the archer decided to break away from his group, and observe his Teach, determined to place that mystery emotion.

He used the key the group found as an excuse for his detour, and put his scheme into action. The key was for a chest, that was being hidden by a group of boulders. It was an obvious hiding spot, but it worked regardless. After he opened the chest, instead of rejoining his group, he stayed there to spy on the scene below.

The very rocks that made the box hard to see, worked perfectly to hide Claude away, from bandits and Byleth alike. The canyon produced a lot of echoes, and helped sounds travel much farther than they could normally. It's only thanks to this, that the noble could not only see the bandits talking to his Professor, but actually hear what they were saying.

"Huh?! You came alone? You're either really brave, or really stupid!"

"Neither," murmured the golden boy, "they're just far more skilled than you."

An archer was hidden behind a pillar next to the boss. While the ex merc's attention was trained on some other scrub charging at them, said archer took the opportunity to fire off (what they likely thought would be) a free shot. Claude wasn't concerned about his Teach being hit, but he was a little worried about how well they could work with divided attention.

He needn't have bothered.

In one fluid motion, Byleth grabbed the arrow flying at them from behind, trained it to their own bow, and used it to shoot down the bandit in front of them, right in the forehead. It happened so fast, so effortlessly, that even the teen watching from afar couldn't process it right away. Though, that didn't stop a shudder from running through him on instinct. A pleasant, excited shudder. While he, and everyone else watching, took their time to consciously register the scene, his Professor kept going.

Another arrow was notched and released, hitting a mage right through their knee. They crumpled to the floor, spell disrupted, screaming in pain, before another arrow finished them off from the other direction. Likely Ignatz, or (even more likely) Leonie, taking the free kill for what it was. While everyone else was distracted by the noise, Byleth kept moving.

When Claude turned back to the ex merc, they had already closed in on the hidden archer, arrows deflected on their way forward. The noble could tell from a glance, that his Teach had no plans of slowing down. They raised their sword to block one last arrow, before swinging it around and snapping the archer's bow clean in half. No longer able to fight, that should have been the end of the encounter. But there was no mercy in his new teacher that day.

The house leader watched on in confusion, as Byleth paused their assault just long enough, to turn the fighting, into a _game._ The thief started begging for their life as the former mercenary stared down at them. They give a quick jerk of their head, the universal signal for "get out of here." Grateful, the archer got up and ran away.

_Or, they would have._

But the moment they turned their back to flee, they were cut down by the very person who gave them hope of a second chance at life. This time, the shudder that ran through the young noble, was one of fear and discomfort <strike>yet somehow, the excitement still persisted</strike>. Unwilling to watch more of the scene unfold, the student ducked down into his hiding place, and chose to just listen to tell when it was over.

"You, what are- Wait, I know you! You were with the Blade Breaker! Then, does that... are you, the Ashen Demon?! N-no! Stay away!"

_Ashen **Demon?**_ Claude did _not_ want to know. No matter how much his curiosity screamed otherwise.

The house leader waited until he couldn't hear fighting from his classmates anymore. Only then did he emerge from his hiding spot, and slide down the shallow cliff to meet with the others. "Looks like that's that. Let's leave the rest to the knights and start heading back." No matter what brave face they had on before, everyone was eager to follow that suggestion.

Everyone except the mercenary. Byleth seemed rooted to their spot, staring into the distance, as if looking for something. Against his better judgement, the teen approached the teacher, wanting to leave this place as soon as possible. "Uh, Teach?"

_"What?"_

Claude took an immediate step back, despite himself. The first hint of emotion he had _ever_ heard in the mercenary's voice, and it was irritation, borderline_ rage._ The mystery emotion he couldn't identify from before. "It's, uh, time to leave?"

For a few seconds, Byleth stared at the noble with unseeing eyes. Eyes somehow _more_ empty than ever before. It all made Claude's heart beat faster, for <strike>mostly</strike> all the wrong reasons. Without responding, the mercenary strode past him. And just that act alone, made his every hair stand on end. Desperate to regain his sense of normal, of _control,_ the teen jogged to the front of the procession. Sliding into the conversation, just in time to poke fun at Lorenz' last statement.

Eventually, the young noble would have to look the teacher in the eye again. But for the time being, he could ignore them. Which was just as well, since Byleth didn't seem to be all there. They kept looking to the side, with their chin down. The same way they did, when listening intently to whoever was talking at them. Were they listening to something? Was there... a voice in their head, maybe? It sounded crazy, but if it were true, it wouldn't surprise Claude at that point.

He felt like nothing the mercenary did, would ever surprise him again. Not after meeting the Ashen Demon.  
. . .

A single day was all it took, for self preservation to be overridden by Claude's overwhelming curiosity.

The longer the young noble thought about it, the less sense it made. Byleth was such a good, helpful, patient, _kind_ person. He had called them goodwill incarnate, and the teen still believed that. So what changed in the canyon? What about that place caused so much anger, and promoted such cruelty? And what, or who, was the teacher listening to as they left?

As before, only one person had the capability of providing him with answers. Which left the teen, once again, standing in front of the Captain's Office. He knew that this conversation with the Blade Breaker wouldn't be as easy. He wasn't asking for clarification, on something everyone else had already noticed. He was digging for information, on a past that he had no right to knowing. It would take incredibly careful wording to get Jeralt to tell Claude anything. But it wasn't his first time interrogating someone, and it certainly wouldn't be his last.

After several steadying breaths, the teen moved to knock on the door. But, "I don't think I've ever seen you like this, Byleth." Just hearing their name sent the noble reeling. He jumped away from the door as if it tried to bite him. "Are you sure nothing happened while you all were out there?"

He should leave, and he knew it. He should walk away from what was no doubt a private conversation. He should stop getting himself so entangled with such a dangerous, mysterious person. Claude knew all of that instinctually. But his curiosity would be the cause of his death, and he'd accepted that fact years ago. So, he parked himself outside of the door, and listened.

"I, I don't know."

"You don't know if something happened?"

"No, nothing happened. At least, everyone else is still okay, but..."

"Are you okay?"

"...I think so?"

"Alright, just breathe, and start from the beginning."

"_sigh_ The moment we stepped into Zanado, I was hit with this sense of, having been there before. It felt like, like coming home after a really long time. The whole place was just so, _nostalgic,_ to me."

"Did Sothis say anything?"

...Sothis? It sounded vaguely familiar to Claude, but he couldn't give a face to the name.

"Yes, mostly she was as confused as I was. The canyon filled her with happiness, and comfort. But also sadness, and betrayal, and _anger._ She was so very angry. The bandits being there made that anger worse."

"Which of course, made you angry in turn."

"Right."

So, Sothis (whoever she was) controlled Byleth's emotions? Is she who the mercenary was listening to as they left that place? The noble would have to try and remember where he'd heard the name from.

"So, what did you do with all that anger?"

"I, took it out on the bandits. Most of the time I struck to hurt, not kill. I toyed with them. I, I'm pretty sure I cut someone's head off, _after_ they were dead."

At this point, Claude was shivering. He understood, rationally, that emotionless was Byleth's default tone. But hearing them talk of _decapitation_ with that even, empty voice, still made him uneasy to his very core.

"Hmm, and when it was all over, how did you feel?"

"...Still angry, still confused. I couldn't calm down until we left Zanado."

"What did Sothis say about it?"

"Well, she thanked me, for killing the bandits. I only stopped being mad because of her gratitude. The canyon was clearly important to us. Uh, to _her,_ but it didn't give her any memories back."

"I see..."

"I'm sorry for bothering you with this all the time."

"Don't apologize. I'm sorry I don't have any answers for you. Now, you still haven't told me what's _really_ bothering you."

Oh gods, there's more?! Claude was confused enough as it was. He couldn't process much more information.

"It's... it's about my students."

"Your brats, huh? What about them?"

"I think one of them saw me, while I was lashing out. I was still angry after the battle, so I didn't realize it. But Sothis told me later, that he was hesitant to approach me. Almost _scared._ And I snapped at him once he did approach, I realized that. He's been avoiding me since we got back. Normally, I wouldn't care if he, or anyone, talked to me or not, you know that. But, I'd never been in charge of someone's safety, someone's _life_ before. If something happens to him because he didn't trust me... I, I don't know how to fix this."

The teacher was talking about Claude. They had to be. And for the second time since they'd met, there was emotion in their voice. _Guilt._ They were guilty about the day before. _Of course they were._ How could the model of goodwill, not feel guilty for scaring someone? How could such an even tempered individual, not feel bad for losing that temper?

With that new perspective at the forefront of his thoughts, the house leader was able to look back to that battle, without a filter of fear covering it. If he was (supposedly) betrayed, in his own home, and then came back to find some common thugs squatting there; Claude would probably be furious. And anger does make a lot of people do regrettable things, by stopping you from caring who you hurt.

The teen recognized that approaching Byleth after the battle, was a bad idea. Yet, he did it anyway. He should have expected to be snapped at. A lot of people stop talking when they're really angry, so of course the former mercenary didn't respond. As for their eyes, well, were they truly emptier than usual? Or was Claude's fear manipulating his perception? No one was rainbows and sunshine 100% of the time, not even his teacher. After thinking over the day again, the whole experience seemed so much, tamer, compared to how it felt as it was happening.

The young noble realized that he might still be wrong. That his desire to see his teacher in a positive light, could be making him overlook some red flags he should pay attention to. That because of his <strike>attraction to Teach</strike> interest in his Professor's backstory, he was pushing down danger signals he would later regret ignoring. **Trusting Byleth was a bad idea.** Wasn't that Claude's instinct from the beginning? He didn't trust easily, and he actively admitted tha-

The teen was so engrossed in his analysis, that he stopped eavesdropping a while ago. So long ago, in fact, that the conversation was over, and his teacher chose that moment to exit the room. "Oh, hello Claude."

The boy in question had to fight off flinching as he turned around. "Oh hey yourself, Teach. Do you have somewhere else to be right now, or can I steal some of your time?" By pure muscle memory, his usual winks and signature smirk whipped back into place. The picture of cunning composure, that Claude had painted himself, masked all trace of his anxiety at being face to face again.

"You... need me for something?" It was obvious that the Professor was blindsided by Claude's complete 180. Squinted eyes were all they needed to communicate their disbelief. Just hours ago he could hardly stand being in the same room as them, but now he's actively seeking them out. Byleth had spent the last few minutes (the part of the conversation Claude stopped listening to) with their father, figuring out how to properly apologize. Yet, somehow, all was already forgiven.

"Well, I don't _need_ you to come with me, but I do _want_ you to check out this new poison I've been creating."

At those words, Byleth's whole being seemed to radiated relief. The teen was telling them that everything was okay now. He wasn't afraid anymore. He was choosing to talk to his Professor again. Not one to analyze the behaviors of others too deeply <strike>yet</strike>, the teacher took their student's peace offering gladly. "Alright, I can spare some time. Where did this new poison come from?"

"I'm glad you asked! So, I discovered a mushroom I'd never seen before, hidden under bushes in a corner of the greenhouse, and- I was careful with the plants around it, don't look at me like that."

As the pair walked downstairs to the classrooms, Claude noted that Byleth's attention was divided. Perhaps that Sothis girl was talking to them again. For once, he chose not to think about it. After being at the Monastery for only a month and a half, the teen had already realized how quickly a normal, quiet day, could become anything else. So instead of looking to the future, like he usually did, he decided to focus on the present. The golden boy had no idea how long he'd have with his Teach, before something went horribly wrong. And so, he planned on making as many good memories as he could, starting right then and there.

Little did Claude know, just how much time he'd truly have with his Byleth.

**Author's Note:**

> I absolutely **hate** how I wrote the end of this (eavesdropping onward), but I've been sitting on it for the whole month, and if I don't post this _right now,_ I never will.
> 
> I also got halfway through this story, before I realized that I somehow didn't once reference Byleth as either gender. I was writing with the girl in mind, but eh, plans changed.
> 
> I wrote this solely for the fact that Byleth was apparently known as the **Ashen Demon**, and it was never mentioned outside of Hanneman's C Support. How do you throw such a badass, mysterious title out there, and then never bring it up again?! It's like, the _only_ continuity issue I've seen so far, and it bothered me so much I _had_ to write about it. Sadly, I'm unable to write anything less than 500 words, and decided to make several references to Jeralt's "no heartbeat" entry, to fill space. <strike>That part slapped me in the face when I read it.</strike>
> 
> My perception of Byleth, wasn't that they are someone with dulled emotions, but rather, dulled expressions. Which is an actual, real world condition (because humans have all types of problems) called **Reduced Affect Display**. "Reduced affect should be distinguished from apathy and anhedonia, which explicitly refer to a lack of emotion, whereas reduced affect is a lack of emotional expression regardless of whether emotion is actually reduced or not." -Wikipedia (thanks Wik!)
> 
> Some people have said that they don't feel like Jeralt and Byleth are very close. I disagree. They're close enough that Jeralt's death made them cry for the first time. You don't cry for the first time in your _entire life,_ for someone you're "not very close to." Jeralt seems to me, like a dad who had a unique kid, was out of his element at first, and then learned how to interact with them over time. They're not particularly warm, but I never felt that they were unusually distant either.
> 
> As for Claude... I could prolly write several pages about Claude. The GD is the first route I finished, and he was the only romance I cared about (which reminds me of a funny video https://youtu.be/XQdrpx8EjN0), so I might be _just a little bit_ biased. I subscribe to the idea that Claude wormed his way into his teacher's heart, purely by never leaving them alone. At first it was just a way of getting close enough to learn their secrets, and use their power, which he readily admits. But it's very difficult to live near someone, fight for your life with them, interact with them _everyday,_ and _not_ grow incredibly close. Also, Claude might have a bit of a thing for dangerous people...
> 
> I'm ranting at this point, so I'll stop here. I have many, _many_ more ideas for this game. Mostly character/relationship studies, involving Byleth, Claude, Dimitri, Jeralt, and Sothis. If anyone cares to see more, let me know.
> 
> For now, comments and feedback (especially about the ending) are very much appreciated. Thanks for reading! ^_^


End file.
